The ultimate objective of this research is to identify each molecular component and elucidate each biochemical process that has a role in the action of antidiuretic hormone (ADH) (vasopressin) in the kidney and toad bladder. Medullary cytosol proteins which are phosphorylated under the influence of ADH in vivo will be identified and compared to those observed previously, in vitro. Fluorescent-labeled luminal membranes from toad bladder will be isolated, fractionated and characterized. Selective chemical modification will be used to identify a protein(s) within the luminal membrane that actively participates in the ADH induced permeability changes. Proteins which span the membrane or are confined to one of its surfaces will also be identified by chemical modification methods. Directed fluorescence experiments with the toad bladder will be used to probe the influence of luminal membrane proteins and other components in the ADH effect. Fluorescence-energy-transfer experiments will be used to test for membrane interactions with a microfilament-microtubule system. Hopefully, these experiments will help elucidate the molecular basis for the fundamental process of regulated water reabsorption by the kidney under the influence of ADH.